A different pathophysiological mechanism is widely accepted for gastric and duodenal ulcer. In particular, the exact role of gastrin in the determinism of nonhormone-dependent peptic ulcer disease has been completely clarified. The aim of the present study was to analyse fasting and postprandial serum gastrin levels in 99 duodenal ulcer patients, 17 gastric ulcer patients and 11 subjects presenting an association of gastric and duodenal ulcer. The possible correlation between postprandial gastrin concentrations and basal and maximal acid output in the 3 groups of patients has also been investigated. Fasting serum gastrin levels do not appear different among the 3 classes of patients, while postprandial gastrin concentrations are statistically higher at 15 minutes in duodenal ulcer patients and in subjects with the association of gastric and duodenal ulcer as compared to gastric ulcer patients. Mean fasting and stimulated gastrin levels are higher in gastric ulcer females than in males during the entire test and with a statistically significant difference at 30 minutes. The concentrations of the hormone are not different in males of the 3 groups of patients at basal time, while they are statistically lower at 15 and 30 minutes in gastric ulcer males compared to those with duodenal ulcer and the association of the localization. Finally, positive correlation has been observed between B.A.O. and M.A.O. and postprandial gastrin concentration in the 3 groups of patients, while there is an inverse correlation between the previous parameters as regards sex, both in gastric and duodenal ulcer.